The present invention is directed generally to a rear projection screen and more particularly to a rear projection screen that incorporates totally internally reflecting structures to disperse the light passing through the screen.
Rear projection screens are generally designed to transmit an image projected onto the rear of the screen into a viewing space. The viewing space of the projection system may be relatively large (e.g., rear projection televisions), or relatively small (e.g., rear projection data monitors). The performance of a rear projection screen can be described in terms of various characteristics of the screen. Typical screen characteristics used to describe a screen""s performance include gain, viewing angle, resolution, contrast, the presence of undesirable artifacts such as color and speckle, and the like. It is generally desirable to have a rear projection screen that has high resolution, high contrast and a large gain. It is also desirable that the screen spread the light over a large viewing space. Unfortunately, as one screen characteristic is improved, one or more other screen characteristics often degrade. For example, the horizontal viewing angle may be changed in order to accommodate viewers positioned at a wide range of positions relative to the screen. However, increasing the horizontal viewing angle may also result in increasing the vertical viewing angle beyond what is necessary for the particular application, and so the overall screen gain is reduced. As a result, certain tradeoffs are made in screen characteristics and performance in order to produce a screen that has overall acceptable performance for the particular rear projection display application.
Thus, there remains a need for screens that have improved overall performance while meeting the minimum performance criteria necessary for the rear projection display application in which the screen is used.
Generally, the present invention relates to a light dispersing film for a rear projection screen and its method of manufacture. The film disperses light passing therethrough by reflecting the light off reflecting surfaces disposed within the film. The reflecting surfaces are formed at the surfaces of structures within the film.
In one particular embodiment, the light dispersing film includes a first layer formed from a first material having a first refractive index, the first layer having first and second opposing sides and a first optical axis normal to the first side. The first layer includes structures formed from a second material having a second refractive index smaller than the first refractive index. The structures have bases at the second side with one or more side walls extending towards the first side. First internal reflecting surfaces are formed by interfaces between the first and second materials. The structure bases include a light absorbing material, and optically transmitting areas of the second side are defined between the structure bases. The first internally reflecting surfaces form reflecting units that asymmetrically disperse light through respective optically transmitting areas. The first reflecting surfaces form surfaces disposed at at least two angles relative to the first optical axis.
In another particular embodiment, the light dispersing film includes a first layer formed from a first material having a first refractive index, the first layer having first and second opposing sides and a first optical axis normal to the first side. The first layer includes structures formed from a second material having a second refractive index smaller than the first refractive index. The structures have bases at the second side with one or more side walls extending towards the first side. First internal reflecting surfaces are formed by interfaces between the first and second materials. The structure bases include a light absorbing material, and optically transmitting areas of the second side are defined between the structure bases. The first internally reflecting surfaces form reflecting units that asymmetrically disperse light through respective optically transmitting areas. The first reflecting surfaces are disposed to reflect light to selected directions within a dispersion plane.
In another particular embodiment, the light dispersing film includes a first layer formed from a first material having a first refractive index, the first layer having first and second opposing sides and a first optical axis normal to the first side. The first layer includes structures formed from a second material having a second refractive index smaller than the first refractive index. The structures have bases at the second side with one or more side walls extending towards the first side. First internal reflecting surfaces are formed by interfaces between the first and second materials. The structure bases include a light absorbing material, and optically transmitting areas of the second side are defined between the structure bases. The first reflecting surfaces form surfaces disposed at two or more angles relative to the optical axis. All light reflected by the first reflecting surfaces is reflected at dielectric-dielectric interfaces.
In another particular embodiment, a film for a rear projection screen includes a substrate layer, having a first substrate layer side. Structures, formed from a first material having a first refractive index, are disposed with structure bases on the first substrate layer side. Sidewalls of the structures extend in directions away from the substrate. Structure bases are formed of light absorbing material. Clear areas are defined on the first substrate layer side between the structure bases. An overlayer, formed from a second material having a second refractive index larger than the first refractive index, is disposed over the structures and the clear areas of the first substrate layer side. Interfaces between the overlayer and the sidewalls form internally reflecting surfaces for light propagating within the overlayer towards the substrate in a direction substantially perpendicular to the substrate.
In another particular embodiment, a light diffusing film for a rear projection screen includes a first layer formed from a first material having a first refractive index, having first and second opposing sides and an optical axis normal to the first side. The first layer includes structures formed from a second material having a second refractive index smaller than the first refractive index. The structures have bases at the second side with one or more side walls extending towards the first side to define first reflecting surfaces. The structure bases include a light absorbing material and optically transmitting areas of the second side are defined between the structure bases. A bulk diffuser is disposed to disperse light passing through the optically transmitting areas of the second side.
In another particular embodiment, a light dispersing film for a rear projection screen includes a first layer formed from a first material having a first refractive index, the first layer having first and second opposing sides and a first optical axis normal to the first side. The first layer includes structures formed from a second material having a second refractive index smaller than the first refractive index, the structures having bases at the second side with at least two side walls extending towards the first side. Internal reflecting surfaces are formed by interfaces between the first and second materials. The structure bases include a light absorbing material, and optically transmitting areas of the second side are defined between the structure bases. At least one structure has at least one of the two sidewalls disposed at an angle selected to be parallel to diverging light passing through the film from an image light source positioned on the first optical axis.
In another particular embodiment of a light dispersing film, the film includes a first film having first and second opposing sides. the first film has a first refractive index within a first refractive index range. The first film includes structures formed from a structure material having a second refractive index smaller than the first refractive index range. The structures have bases at the second side with one or more side walls extending towards the first side. First internal reflecting surfaces are formed by interfaces between the structure material and the material of the first film. The structure bases include a light absorbing material, and optically transmitting areas of the second side are defined between the structure bases. The first refractive index of the first film proximate the first side is different from the first refractive index of the first film proximate the second side.
In another particular embodiment, the light dispersing film includes a first layer formed from a first material having a first refractive index, the first layer having first and second opposing sides and a first optical axis normal to the first side. The first layer includes structures formed from a second material having a second refractive index smaller than the first refractive index. The structures have bases at the second side with one or more side walls extending towards the first side. Metal coatings are disposed on at least portions of the side walls between the first and second materials to form first reflecting surfaces. The structure bases include a light absorbing material, and optically transmitting areas of the second side are defined between the structure bases. The first reflecting surfaces form reflecting units that asymmetrically disperse light through respective optically transmitting areas. A bulk diffuser is disposed within the first material to disperse light passing through the optically transmitting areas of the second side.
A particular method for manufacturing an optical film includes casting and curing structures on a substrate, the structures being formed from a first material having a first refractive index and with optically absorbing bases on the substrate, and open substrate areas being defined between adjacent structures on the substrate. The method also includes overcoating the structures and the open substrate areas with a second material having a second refractive index greater than the first refractive index, so as to form reflecting surfaces at interfaces between the first and second materials. The reflecting surfaces are disposed to reflect light, propagating through second material substrate in a direction substantially parallel to an optical axis of the film, towards open substrate areas.
Another particular method of forming an optical film includes forming grooves on a first side of a film of first material having a first refractive index, with open areas of the first side between the grooves. The method also includes forming an optical scatterer on the open areas of the first side, and filling the grooves with a second material having a second refractive index smaller than the first refractive index, the second material being optically absorbing.
Another particular method of forming an optical film includes casting and curing structures on a substrate, the structures being formed from a first material and with optically absorbing bases on the substrate, and open substrate areas being defined between adjacent structures on the substrate. The method also includes disposing a metallic layer over at least part of the structures to form reflecting surfaces and overcoating the metallic layer and the open substrate areas with a second material. The reflecting surfaces are disposed to reflect light, propagating through second material substrate in a direction substantially parallel to an optical axis of the film, towards open substrate areas.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.